Glycolysis and gluconeogenesis are central pathways of metabolism across all domains of life. A prominent enzyme in these pathways is phosphoglucose isomerase (PGI), which mediates the interconversion of glucose-6-phosphate and fructose-6-phosphate. The predatory bacterium Bdellovibrio bacteriovorus leads a complex life cycle, switching between intraperiplasmic replicative and extracellular ‘hunter’ attack-phase stages. Passage through this complex life cycle involves different metabolic states. Here we present the unliganded and substrate-bound structures of the B. bacteriovorus PGI, solved to 1.74 Å and 1.67 Å, respectively. These structures reveal that an induced-fit conformational change within the active site is not a prerequisite for the binding of substrates in some PGIs. Crucially, we suggest a phenylalanine residue, conserved across most PGI enzymes but substituted for glycine in B. bacteriovorus and other select organisms, is central to the induced-fit mode of substrate recognition for PGIs. This enzyme also represents the smallest conventional PGI characterized to date and probably represents the minimal requirements for a functional PGI.

糖酵解和糖异生是生命各个领域代谢的中心途径。这些途径中的一个重要酶是磷酸葡萄糖异构酶 (PGI)，它介导 6-磷酸葡萄糖和 6-磷酸果糖的相互转化。捕食性细菌Bdellovibrio bacteriovorus导致复杂的生命周期，在周质内复制和细胞外“猎人”攻击阶段之间切换。通过这个复杂的生命周期涉及不同的代谢状态。在这里，我们展示了B. bacteriovorus的未配体和底物结合结构PGI，分别解析为 1.74 Å 和 1.67 Å。这些结构表明，活性位点内的诱导拟合构象变化不是某些 PGI 中底物结合的先决条件。至关重要的是，我们建议苯丙氨酸残基，在大多数 PGI 酶中保守，但在B. bacteriovorus和其他选择的生物体中取代甘氨酸，是 PGI 底物识别的诱导拟合模式的核心。这种酶也代表了迄今为止表征的最小的常规 PGI，并且可能代表了对功能性 PGI 的最低要求。